With the development of the information society, the traffic of information is dramatically increasing. With the increase, optical communication, which enables fast and high-capacity transmission, is becoming widely used. Because of the growth of the social importance of information-communication, there is a growing demand for reliable communication networks.
Various techniques are being developed in order to accommodate the increase in traffic and meet the demand for reliability of communications in the field of optical communication. On the other hand, as a result of attempts to configure high-capacity and reliable networks, the configurations of networks are becoming more and more complicated and the number of optical transmission devices used are increasing. Consequently, the power consumption in optical network systems and optical transmission devices used for the networks are increasing. Accordingly, the importance of optical network systems capable of power saving while maintaining reliability and optical transmission devices used for such optical network systems is increasing and related techniques are being actively developed. For example, PTL 1 discloses a technique for improving the reliability of optical transmission devices.
PTL 1 describes a wavelength-division-multiplexing-based optical transmission device including a backup optical transceiving unit. The optical transmission device in PTL 1 includes separate optical transceiving units for high speed communication and low speed communication and a backup optical transceiving unit designed to the same specifications as those of the optical transceiving units used for high speed and low speed communications. The optical transmission device has monitoring and control functions for detecting failures or the like in the optical transceiving units. When a failure of in an optical transceiving unit is detected, switching is done to the backup optical transceiving unit. The provision of the backup optical transceiving units in the optical transmission device enables quick switching in the event of a failure.
Power saving techniques for optical network systems such as a technique in PTL 2 are disclosed. PTL 2 discloses a technique relating to power saving in interface units of an optical network system. The optical network system in PTL 2 includes an interface units associated with backup paths. The interface units associated with the backup paths are placed in a power saving mode when a backup path is chosen and, when a failure occurs, the interface units exit from the power saving mode and are used for communication in a normal active mode. PTL 2 claims that the function of putting the interface units of the backup path on standby in the power saving mode allows power saving of the entire network system.
PTL 3 discloses a technique that controls the timing of supplying power to optical transceiving units in an optical transmission device made up of a plurality of optical transceiving units. The optical transceiving units in PTL 3 have a normal operation mode and two power saving modes. When the optical transceiving units are switched from a power saving mode to the normal operation mode, the timing of supplying power to the optical transceiving units is controlled. PTL 3 claims that a malfunction can be avoided by controlling the timing of switching the optical transceiving units to the normal mode to prevent an abrupt voltage drop.